Comparison of two formulations of DDT as dipping fluids for the control of the cattle tick

Abstract

Fertile cattle ticks matured on cattle dipped at fortnightly intervals in 0.5 per cent. pp'-DDT as a wettable powder preparation; but none matured on cattle dipped at fortnightly intervals in 0.5 per cent. pp'-DDT as a "colloidal" preparation, although numerous larval ticks attached to the cattle between dippings. This difference in performance was considered to be due largely to pronounced differences in the amounts of DDT left on the hair of the cattle by the two formulations. Hair samples clipped from cows immediately after dippings in the wettable powder carried more or less uniform amounts of DDT throughout the series of dippings. The quantities of DDT deposited on the hair by the freshly prepared "colloidal" fluid were of the same order as those from the wettable powder; but there were greatly increased deposits at subsequent dippings, particularly those carried out a fortnight after fresh concentrate had been added to the vat. Cattle dipped in both formulations removed more DDT from the vat than could be accounted for by the volume of fluid contained in the hair. This "stripping" effect was most marked in the older "colloidal" preparations. The amounts of DDT remaining on the hair a fortnight after dipping were of the same order in both preparations, and showed a progressive increase with the increasing age of the dipping fluid.